1. Field of the Invention
The present invention generally relates to a touch panel, and more particularly, to a surface acoustic wave (SAW) touch panel capable of reducing a back wave generated from a surface acoustic signal wave therein.
2. Description of the Prior Art
Electronic devices are generally not inputted by voice or handwriting, which are intuitive to humans, but a keyboard or a mouse. Such inputting through the keyboard or mouse is not made in a direct sense and would possibly form a barrier for those who are not familiar with operations on the electronic devices. In this regard, more intuitively operated inputting devices and methods have been expected to be used on the new electronic devices. Touch panel is one of these promising inputting devices.
Touch panel has the simplest user-machine interface among those of the currently available intuitively inputting devices. In operation, an object, normally a stylus or a finger of a user, touches the panel and a position of the touch is determined. Then, when continuous touch positions (in some cases) are obtained, a corresponding input is thus formed. With the provision of the touch panel, it is relatively easier for the user to input to an electronic device by the intuitive sense based inputting method other than the keyboard and mouse lacking of the intuitive basis.
In general, a touch panel is a glass substrate constructed by a conductive glass and a conductive film, through which images are displayed on a touch screen thereof with the aid of associated control ICs on a printed circuit board (PCB) provided therebelow. A touch panel has the humanized input interface characteristic and thus requiring the least teaching and learning for man. That is, the user can directly input instructions by a finger or touch pen, etc., through the touch panel according to the function indication shown on the screen. The touch panel may be broadly applied onto, for example, eBook, global positioning system (GPS), personal digital assistant (PDA), WebPhone, notebook, Web Pad, handheld PC, etc.
In general, the touch panel are classified into at least four types: resistive, capacitive, IR, and surface acoustic wave (SAW) touch panel. The SAW type touch panel employs acoustic waves propagating in a substrate surface. When an object touches the surface, the propagation of the specific acoustic waves associated therewith will be blocked. By detecting this sudden change, the location on the touch panel touched by the object can be determined. Referring to FIG. 1A and FIG. 1B, which respectively show a vertical view and a 3D diagram of a conventional SAW type touch panel 100. As shown, the touch panel 100 includes a substrate 104 having a first side 106, a second side 108, a third side 110 and a fourth side 112 together defining a surface 104; and an X-axis transmitting transducer 114, an X-axis receiving transducer 116; a Y-axis transmitting transducer 124 and a Y-axis receiving transducer 126. Each of the transducers 114, 116, 124, 126 has a plurality of reflectors formed therein, which are not uniformly arranged in the respective reflecting stripes 114, 116, 124, 126, exactly, from thinness to thickness when viewed in the propagation direction of the unreflected surface waves, which will be appreciated after the following context is read. The described receiving transducers 116, 126 are devices which can transform a mechanical energy to an electrical energy by a piezoelectric material, and vice versa. As generally known to those skilled in the art, each of the transducers 114, 116, 124, 126 may have a wedge or comb form.
As shown in FIG. 2, it is a case where the wedge formed transducer 230 is used, where a shear wave is transformed into a surface wave. In FIG. 2, the reference numeral 232 represents the piezoelectric material, and the arrow indicates the propagation direction of the surface wave. As shown in FIG. 3, it is another case where the comb formed transducer 330 is used, where a longitudinal wave is transformed to a surface wave, which is propagated in the direction indicated by the arrow, and the reference numeral 332 represents a piezoelectric material. Referring back to FIGS. 1A and 1B, the substrate 104 further includes reflecting stripes 190, 191, 192, and 193. The surface wave produced by the X-axis transducer 114 is transmitted along the −x direction and then the +y direction when being reflected by the reflecting strips 193, where some surface waves are caused to occur. Then, the reflected surface waves proceed along the +x direction when encountering the reflecting strips 191. Finally, the surface waves are received by the X-axis receiving transducer 116 and transformed into electrical energy thereby. Similarly, the surface wave produced by the Y-axis transducer 124 is transmitted along the −y direction and then the +x direction after being reflected by the reflecting stripes 192, where some surface waves are caused to present. Then, the reflected surface waves proceed along the +y direction when encounter the reflecting stripes 190. Finally, the surface waves are received by the Y-axis receiving transducer 126 and transformed into an electrical energy.
Take the X-axis as an example, referring to FIG. 4 and FIG. 5, FIG. 4 illustrates a voltage wave Vx of the electric energy generated from the X-axis receiving transducer 116 when no any object touches on the surface 104 of the touch panel, and FIG. 5 illustrates a voltage wave Vx of the electric energy generated from the X-axis receiving transducer 116 when an object touches on the surface 104 of the touch panel. As can be appreciated, the presence of the object leads to an absorption of a large portion of the surface wave energy existing thereunder, and a corresponding voltage drop is thus created on the voltage wave Vx. This voltage drop can be relied upon to deduce the Y-axis position of the object on the substrate 104 of the touch panel based on the fact that different surface waves associated with the X-axis transmitting and receiving transducers 114, 116 and different reflectors of the reflecting stripes 191, 193 have different times before being received at the receiving transducer 116. Likewise, a voltage wave Vy in relation to the X-axis position of the object touching on the substrate 104 of the touch panel 100 also exists although not shown in the figures. However, the surface wave does not ideally proceed in a straight direction but somewhat diverges, like that of an optical beam. At this time, when the surface wave is transmitted to an edge of the substrate, a back wave due to discontinuity at the edge is generally generated. The back wave interferes with the propagation of the component of the surface wave still under the corresponding reflecting stripe, and accordingly adversely affects the accuracy of position detection. Therefore, there is a need to provide a touch panel with an improved touch position determining capability.
From the above it is clear that prior art still has shortcomings. In order to solve these problems, efforts have long been made in vain, while ordinary products and methods offering no appropriate structures and methods. Thus, there is a need in the industry for a novel technique that solves these problems.